As a method for obtaining a high-refractive index material, there has been known a method involving introducing a sulfur atom into an organic compound, a method involving forming a composite by combining inorganic particles each made of titanium oxide, zirconium oxide, or the like with an organic component (such as a polymer), or the like. However, the introduction of a large amount of the sulfur atoms may cause an odor problem or a reduction in stability due to a disulfide produced as a byproduct from an impurity in a raw material. Further, a composite of the inorganic particles and the organic component may cause a problem in association with the agglomeration of the particles (such as a reduction in transparency).
In addition, an attempt has been made to introduce an aromatic skeleton to obtain a high-refractive index material. In particular, a fluorene skeleton (9,9-bisphenolfluorene skeleton) out of the aromatic skeletons has characteristics such as a high refractive index and high heat resistance, and hence a high-refractive index material using a compound having such fluorene skeleton has been studied.
For example, Patent Document 1 discloses a photopolymerizable resin composition containing an epoxy resin having a fluorene skeleton (such as bisphenol fluorene diglycidyl ether or a 9,9-bis(glycidyloxy C2-4 alkoxyphenyl)fluorene), an alkoxysilane, and a photoacid generator. In addition, Patent Document 2 discloses a high-refractive index material obtained by curing a polymerizable composition containing a fluorene compound, a metal alkoxide, and a photoacid generator.
However, any such high-refractive index material using a compound with a fluorene skeleton uses a photoacid generator, and hence concern has been raised about a reduction in transparency due to the remaining of the generator.
Further, a photosensitive resin composition has been used in: the formation of a protective film for preventing the deterioration of, or damage to, an electronic part such as a TFT-type liquid crystal display device, a magnetic head device, an integrated circuit device, or a solid-state imaging device; the formation of an interlayer insulating film for insulating a gap between wirings placed in a layer manner; the formation of a microlens or a microlens array; or the formation of an optical waveguide. The photosensitive resin composition is required to have excellent transparency and to have a high refractive index from the viewpoint of a concentration.
Patent Document 3 discloses a composition comprising: a copolymer containing hydroxyphenyl (meth)acrylate and an epoxy group-containing unsaturated compound as polymerizable components; and a quinone diazide group-containing compound, as such a photosensitive resin composition. However, the refractive index of the composition is low and its transparency is insufficient.
Patent Document 1: Japanese Patent Application laid-open No. 2005-314692
Patent Document 2: Japanese Patent Application laid-open No. 2011-190179
Patent Document 3: Japanese Patent Application laid-open No. 2007-033518